ABSTRACT
This chapter aims to discuss the interrelated mechanisms responsible for facilitating fecal continence and normal defecation. Voluntary control of defecation is essential for normal social well-being. Preservation of continence depends on the integration of numerous complex anatomic and physiologic mechanisms. The mucosa of the anal canal proximal to the dentate line is richly supplied with sensory nerve endings responsive to tactile, thermal, and painful stimuli and is important for distinguishing the character of rectal contents. An acute increase in rectal pressure causes the rectal muscularis to contract slightly, while the internal anal sphincter relaxes and the external anal sphincter contracts. Rectal distension is perceived once stool enters the rectum. Subconsciously, the recto-anal sphincter inhibition response occurs and the nature of the rectal contents is discriminated by the proximal anal canal. The viscoelastic properties of the rectal muscularis which mediate these relationships have been quantified using an electronic barostat.
